Typically, in the manufacture of gypsum board, for example a paper faced wall board as used in dry wall construction, a pregenerated foam is added to the board slurry mix. This foam is generated from a mixture of a liquid foaming agent, air and water in a suitable foam generating apparatus. The foamed gypsum slurry then is deposited upon a moving paper or other substrate supported on a long moving belt. A second substrate then is applied on top of the slurry to constitute the second face of the gypsum board. Next, the sandwich passes through a forming station which determines the width and thickness of the gypsum board. In a continuous operation, the gypsum slurry begins to set immediately after the board is formed. Subsequently, the board is dried, cut and bundled into commercially acceptable lengths.
Recent attempts to improve gypsum board by reducing its weight without reducing strength include producing numerous, small foam voids in the gypsum core. To do this, the industry typically uses a foaming agent which includes oligomers of alkyl sulfates and alkyl ether sulfates. See U.S. Pat. Nos. 5,240,639 and 5,158,612.
Another recent attempt to improve gypsum board goes in the opposite direction and creates large foam voids in the gypsum rather than small ones. See U.S. Pat. No. 5,085,929.